This invention relates in general to sewing machines and, in particular, to a new and useful buttonhole sewing machine, comprising a stationary lower part, an arm which is pivotally mounted on the lower part and movable from a fixable sewing position into a rest position in which it is turned away from the stitch-forming area, a rotary hook which cooperates with a needle guided in the lower part and penetrating the work from below upwardly, a buttonhole cutting mechanism, a thread monitoring equipment, a displaceable work clamp including a base clamping part which is mounted on the lower part and rests against a resilient support and a top clamping part which, in the sewing position of the arm, rests against the arm.